A known image forming apparatus may include a housing defining a sheet conveyance path in which a sheet is conveyed, and a transfer belt disposed in the sheet conveyance path within the housing. The transfer belt circulates and has a transfer surface. The transfer surface is a flat surface which extends in a width direction of a sheet to be conveyed and is inclined slightly with respect to a horizontal direction.
The image forming apparatus includes four photosensitive members and four respective developing units. The photosensitive members are disposed facing the transfer surface from below in the housing and arranged in a longitudinal direction of the transfer surface.
In the image forming apparatus, each developing unit supplies a developer onto an electrostatic latent image formed on a corresponding photosensitive member to form a developer image. The developer image is transferred from each photosensitive member to the transfer surface, and then transferred onto a sheet being conveyed in the sheet conveyance path. In this way, the image forming apparatus is configured to form an image on a sheet.
In the image forming apparatus, even if each developing unit could be replaceable, it is liable to interfere with the transfer belt, the photosensitive members and other elements disposed in the vicinity of each developing unit, and it seems like replacement of each developing unit is not easy. To improve maintenance, it is required that developing devices are replaced easily.